Selection of automatic control valves
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How to choose an automatic control valve? When contacting the manufacturer, do I need to provide the pressure difference before and after the valve? What is the use of the pressure difference? Is it better to choose a linear or equal percentage flow characteristic? Are there any other parameters that need attention? I hope you will kindly offer your guidance
What you need to provide for him are the medium, temperature, pressures before and after the valve, leakage requirements, as well as any other specific requirements you might have
Reply to 2# arita: Why is it necessary to provide the pressure difference before and after the valve? What impact does it have on selecting the valve? The problem is that I don’t know the pressure after the valve; I only know the pressure before it. Is the pressure after the valve determined by oneself?
If you are a control valve used to regulate performance, then the pressures before and after the valve are important; the purpose of measuring these pressures is to determine whether the pressure difference between them is large or small. A larger pressure difference means higher flow rates, and this plays an important role in determining the appropriate valve size. As for whether equal percentage control or linear control is better, it really depends on how much the flow rate varies. Equal percentage control is generally the most commonly used approach!
You are inquiring about pneumatic control valves, right? A pressure difference needs to be provided. Pneumatic control valves all have a maximum allowable pressure difference; if this difference is too large, the pneumatic actuator is unable to overcome the backpressure and open or close the valve.
Reply to 3# fang410: If you know the pressure before and after the valve, it’s possible to calculate the unbalanced force on the valve, which makes it easier to select the appropriate actuator model. You also need to provide him with the flow rate, so that he can decide on the valve size as well as whether the control should be linear or proportional. Let him make those choices
Reply to 5# 000123a: I’m asking about electric control valves. They also require a pressure difference, but is it up to me to determine this value? A pressure of 2 MPa before the valve and 1.95 MPa after it is acceptable; 1.96 MPa is fine as well, and 1.97 MPa is okay too. In short, the pressure after the valve doesn’t need to be determined with great precision. How should I make my choice?
It’s fine as long as it works; it depends on your system requirements
The pressures before and after the control valve are used by the valve manufacturers to calculate the diameter of the valve core. Knowing the pressure behind the valve allows for an approximate estimation of that pressure; generally, a value that is midway between the system pressure behind the valve and the pressure in front of the valve is taken as an estimate. The manufacturer of the control valve also needs to be provided with information on the medium, density, and temperature in order to determine factors such as corrosivity and operating temperature.
Reply to 9# chinazwr: If I choose a pressure difference of 0.04 MPa before and after the valve, will the actual pressure difference before and after the valve be around this value during operation? Is the pressure difference before and after the valve I selected the one at full opening of the valve, or something else?